You can adapt a focusing screen for a different camera and different size. Here's how.

When I bought my Hartblei HCAM B1 used on ebay, the focusing screen that came with it was somewhat scratched. But what bothered me more: the fresnel on that screen was so coarse that it was very hard to actually focus. I also found the screen to be quite dark. Therefore I decided to replace it.

The aluminum frame around the screen on the HCAM reads "for Hasselblad", so I assumed that the camera will work with any Hasselblad V-series screen (both are medium format after all), and I found myself a nice Beattie focusing screen for Hasselblad on ebay.

I was mistaken however: the "for Hasselblad" on the HCAM relates to the viewfinder, not to the screen. As you can see on the next photo, the original focusing screen from the HCAM is slightly bigger than a Hasselblad screen, so my new screen would fall through :(

I considered returning the screen or replacing the aluminum frame, but I finally decided to simply adapt the focusing screen and make it fit.

First I removed the actual fresnel from its metal frame. I also removed the clear glass that covered it. The grid on that glass doesn't correspond to my digital back's sensor area anyways, so I left it out altogether.

A new frame for the focusing screen

Next, I needed to make a new frame for the fresnel with the inner dimensions of the Hasselblad fresnel and the outer dimensions of the HCAM's screen mount. I decided to cut that from acrylic with a laser cutter.

I also considered pouring resin instead of cutting from solid material. That would have bonded well with the fresnel's edges. But I didn't want to take the risk of resin spilling onto the surface of the screen, so I cut from acrylic.

If you don't have access to a laser cutter, of course you can also cut the material with a saw and a file. It just takes a bit longer.

You can see the frame on the top left of the above photo. That's the part which will hold the fresnel and fit into the camera. On the bottom, you can see the material I cut it from.

I measured the fresnel's thickness to be 2mm, so I looked for any acrylic on stock with that thickness. By coincidence, the material I still had happened to be 2mm grey translucent acrylic... and that gave me yet another idea:

I decided to cut a second piece of acrylic, again with the same outer dimensions (to fit in the camera) but the inner dimensions of the CCD sensor in my digital back, a PhaseOne P40+. That second frame sits above the fresnel for another important purpose: in the view finder, it frames the edges of what the sensor can capture, by covering whatever is outside the frame. But since it's translucent, it still allows the photographer to see what's beyond the frame, albeit darkened by roughly 1 f-stop. Rather awesome!

The fresnel needed to be fixated in its new frame. Plastic glue did the job. The distance from the lens to the focusing screen is obviously quite important: it needs to be the same as with the sensor (to ensure that the same area is sharp). But the engineers at Hartblei already solved that issue; I just had to make sure that the fresnel was accurately level with the frame - and to ensure that, it was enough to place it on a flat surface with the underside before glueing it.

For glueing, I used Ruderer L350, a glue that bonds very well with plastics and hardens in less than a minute. Dispensing it accurately is always a challenge, so I used an injection needle for that.

The seams of glueing are nice enough but certainly visible. That's irrelevant though. They are so far outside that not only are they beyond the sensor area, they are even beyond what's visible through the viewfinder.

Installing the focusing screen

The adpated focusing screen fits perfectly into the camera. The cop cover is re-installed. It holds the focusing screen in place and later holds the viewfinder.

Two pieces of shrink wrap help to keep the focusing screen absolutely tight. You can see one on the top of the above photo. The one on the bottom is already in place under the steel frame.

Looking though the viewfinder now gives a much nicer preview than before. It also shows the edges of the PhaseOne sensor. I tried to capture the view below.

This photo above was taken through the actual lens of the viewfinder, which was hard to photograph. When you look through with your eye, it's nice, big, sharp and bright, and without the vignette.

The photo below was taken of the back of the camera with the viewfinder taken off. Compared to the light on the back of the camera itself, you can already guess how bright the screen is (aperture was 2.8 and the photo was turned upside down).

How to adapt a focusing screen

Let's resume how to adapt a focusing screen.

Of course, the screen you want to adapt needs to be at least the size of your film/sensor or bigger. In my case, it was bigger than my sensor but smaller than the mount in the camera. To increase the size, you can make a frame from acrylic with the outer dimensions of the camera mount and the inner dimensions of your screen. Glue it in place. Make sure screen and frame are level and take care not to blemish the surface of the screen.

If your screen is bigger than your film/sensor but also too big to fit into the camera and you cannot (or don't want to) modify the camera, you need to make the screen smaller. Most screens are made from plastic or resin. They can carefully be cut with a utility knife (use a metal ruler on the to-be-removed side and cut multiple passes). Some screens are sandwiched from clear or ground glass and fresnels or microprism elements made out of resin. For the resin parts, proceed as described. Glass can be carved and broken, but for such small and fragile parts, your best bet is probably to have a fresh piece of plain glass cut for you in the proper dimensions. That is very inexpensive because plain glass doesn't cost much. You can even do without the glass, as a flat glass cover makes no optical difference. It's only easier to clean.

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To make your own custom parabolic reflector in any size or depth out of tissue, you need to calculate the shape of the tissue segments and where to sew it. I did the math for you… here is how.

Tools

To make your own custom parabolic reflector in any size or depth out of tissue, you need to calculate the shape of the tissue segments and where to sew it. I did the math for you… here is how.

Tools

For my calculation I used the program „Grapher“ which comes for free with every Mac. Few people know it although it is quite powerful. Those of you who use a Mac can download my grapher file below and calculate your own reflectors within minutes. For everybody else I have included all the formulas so you can use a program of your choice or even pen and paper.

Constants

Any parabolic reflector can be defined by two numbers: the diameter and the depth. Since the tissue is flat and the reflector is composed of multiple segments, we also need the number of rods:

My sample reflector has a diameter of 1100 millimeters, but you can actually use any unit you like with these formulas (centimeters, inches, …) and obtain correct results.

From these constants we derive two more constants:

The radius is simply half the diameter. m is the parabola constant (i.e. the factor in the parabolic equation z=mx^2.

Calculating the bent rods

The rods (the bending parts defining the shape of the parabola) can be calculated as a series in Grapher: by using the notation {0..rods} we enforce a rod to be calculated for every whole number in the interval.

Since the rods face away from the center in a circular pattern, we can calculate their points using trigonometric functions (sin, cos). The projected length of a rod (i.e. the projection of the rod to the ground plane with all Z values being zero) is simply the radius. The actual Z value finally is our parabolic function, since the rod is bent according to a parabola.

With these values we can have Grapher draw the (bent) rods:

To get a more realistic plot, we want to draw the outer rim by connecting the endpoints of the rods. This can be done by the following equation:

Calculating the focal point

That’s easy: the focal point of a parabola is at z = 1 / 4m.

The above equation tells Grapher to draw the focal point as a little ball in the diagram. For our example reflector, the focal point is roughly 108 mm inside the reflector.

Unbending the rods

But how long are the rods really, and which shape does the tissue need to have? To answer these questions, we first have to calculate a flat (unbent) rod. Mathematically speaking, we need to determine the arc length of the parabola from the vertex to the outer rim.

For a function f(x), the arc length in the interval from a to b can be calculated as

where f’(x) is the first derivative of the original function. That means for our parabola:

Solving the integral and re-formulating this in Grapher syntax gives:

rodLength is the total length of a rod (from the vertex to the outer rim). rodRunLength is essentially the same but uses the variable prjLen (the projected length) which covers all values from 0 to boxRadius, i.e. all points along the rod. Basically, rodRunLength is a function of prjLen which tells us for any projected point on the ground plane how long the bent rod actually is from the vertex to the point above this projected point.

Now we know how long a segment of tissue needs to be, but not yet how wide it needs to be. But that is not difficult. We can use Pythagoras and simply determine the distance between two points on adjacent rods:

For a tissue segment, segWid gives the width for any projected point, while rodRunLength gives the length at which the rod has that width. In order to graph this, I made a new Grapher document with only 2 dimensions (like the tissue). The following equation plots the side walls of a tissue segment:

The segment is symmetrical. I used the variable sg to plot both side walls instead of just one.

This equation draws the top wall of the tissue segment (i.e. the outer rim).
And this is what it looks like:

By stitching 16 of those together, you get the 3D parabola.

Generating different reflectors

Now you can generate a multitude of different reflectors. All you have to do is modify the three key parameters to your liking:

boxDiameter

boxDepth

rods

Here are some configurations for your inspiration:

Download the math files

Calculate reflectors online (JavaScript)

If you are super-lazyefficient, you can even calculate the tissue right here on this page, because I put the formulas into JavaScript for you. Just modify the 3 constants below to your liking and the page will generate two series of points: one for the rod (i.e. the reflector seen from the side) and one for the tissue segment (i.e. the curve you need to mirror and cut out of tissue to get one segment. Assemble all the segments to get the parabolic reflector).

Diameter

Depth

Rods

Curve resolution

m

Focal distance

Rod length

Rod curve

Tissue curve

By the way: you can easily generate the drawing in AutoCAD by typing pline, pressing enter and copying the series of points from this page into AutoCAD.

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To tilt a flash (or light modifier) up and down on a light stand, you need a swivel / pivot clamp. They are either light (but not sturdy) or robust (but heavy), so I made my own medium duty swivel: light and robust.

Why make one?

To tilt a flash (or light modifier) up and down on a light stand, you need a swivel / pivot clamp. They are either light (but not sturdy) or robust (but heavy), so I made my own medium duty swivel: light and robust.

Why make one?

There are basically two types of tilters available:

The small swivel weighs around 300g (this model 380g / 13oz) and is typically used to tilt speedlites and umbrellas. But with a specified payload of 2kg (4.4 lbs), it is not robust enough to carry much more.

The heavy duty pivot clamp is typically used for boom arms. It can carry an elephant, but it weighs 800g (2 lbs) itself and is too heavy for many applications where elephants are not involved.

What's clearly missing is something in between the two. A swivel that can carry most flashes and big light modifiers, while weighing considerably less than the super heavy duty version. May I introduce... the medium duty pivot clamp!

My design

My swivel consists of 3 parts CNC milled from 5mm Aluminum: the middle part that gets attached to the flash, and two side parts that get mounted on the light stand. For the mount, I decided to use a female spigot adapter, simply because I had an unused one. It would also be easy to make one, but that would require more than 3 layers of 5mm Aluminum because the hole for the spigot has a diameter of 16mm.

It is designed to pivot over an angle of 90°: up to 30° upwards and 60° downwards, which should be enough for most applications.

Ex-center screw for robustness

Robustness depends on two factors: of course the material has to be thick enough if you don't want it to bend under the weight. But the other important factor is the location of the screw that holds the pivoted part in place. As you can see above, a single screw (with a lever) functions as the pivoting axis and the point of fixation of the small swivel. With such a design, the swiveling part can easily get loose, because at the center point, the force caused by the payload's weight is at its maximum, with a minimum distance. By contrast, the heavy duty design (right picture) sports a seperate locking screw away from the center, where considerably less force is required to hold the payload in place. That is the key to sturdyness!

...so, of course, my swivel uses an ex-center locking screw

Assembly

The finished swivel

Tilt range

Weight and payload

My swivel weighs only 305g (10.75oz). That is well in the range of the small swivels, even lighter than the small Manfrotto. However, thanks to its construction, it can carry much more weight without losing its position. I did a little test with two steel weights (6kg / 13 lbs in total). The swivel stayed perfectly in position and did not slide down a bit. It would probably also support 10kg if you tighten the screw, but in anycase it is robust enough for most typical payloads.

I wonder why Manfrotto doesn't make these yet :)

...and if you want to know what the heck THAT is, keep reading my blog :)

Attachment of payload

Jeremy over at DIY Tripods asked how a light modifier is actually attached to the swivel. Taking a photo of that is tricky, since the screws are hidden inside the construction and there is no perspective that would show all of them. But I have an x-ray sketch for you! There are two screws (blue in the sketch) that connect the modifier to the swivel. The M6 screw goes through it, the M4 screw goes deep within. And to prevent that one from bending, I have put a plastic part on each side of the swivel (labeled POM). I hope it becomes clear.

Yes, I admit: a standard spigot would have been a more versatile connector on that side as well. However, I want to use the swivel to tilt other DIY equipment that doesn't have a spigot anyways, so I opted to mount it directly, hence the exotic shape.

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I made my own DIY focusable deep parabolic reflector based on a softbox. In this article I describe how to make a speedring adaptor with a slidable tube that allows moving a flash head in and out of a the reflector, how to mount a flash head on the tube,

I made my own DIY focusable deep parabolic reflector based on a softbox. In this article I describe how to make a speedring adaptor with a slidable tube that allows moving a flash head in and out of a the reflector, how to mount a flash head on the tube, and how to mount the reflector on a light stand without affecting the focusing mechanism.

Why the tube

When using a softbox, the flash is usually mounted in the speedring. That would put it into the vertex, which is obviously not what we want. To be able to move the flash head in (towards the vertex) and out (away from the vertex) of the reflector, we need a tube. And we need to

mount the flash at one end of the tube, facing the tube, and

mount the tube in the speedring and make it slidable

A focusable parabolic reflector is a light modifier with a parabolic shape that can be focused, i.e. the light source can be moved within the reflector. This allows very different light characteristics ranging from focused to wide-open. Besides this unique flexibility, other advantages of focusable parabolic reflectors are their high energy efficiency and the relative absence of hotspots.

Attaching a bayonet mount

I decided to use a real bayonet (as opposed to clamps or tie wraps) for flexibility and easy (dis)assembly. My flash of choice for this reflector is the Elinchrom Quadra. I considered using a Lastolite Quadra plate for this purpose, but finally opted for the bayonet part of an RQ-EL adaptor that I had taken apart. That part comes with a very short reflector.

Note that although it looks bigger on the photo, that reflector is a mere 17mm (⅝") deep - considerably shorter than even the small standard reflector. Thus it merely shields direct light from the subject but does not do much in terms of directing the light. That's just what we need.

Of course, the mount needs to face backwards, into the reflector. And of course it needs to be "in the middle" (on the axis). To attach it, I used three threaded rods with M3 threads. I could have simply fixed them on the bayonet with two nuts each, but instead I opted for bolts with an inner thread and additional screws through the bayonet into the bolts. That allows me to fine-adjust the length of each rod by turning the bolts.

To attach the rods to the tube, I used a round piece of wood that I shoved into the tube (after widening the tube just a tiny bit with a hot air gun). I drilled three diagonal holes into the wood and screwed the rods in place, with a little bit of glue to be sure.

Notice the little screw sticking out from the wall of the pipe. That one has nothing to do with the wood or the rods. I added this screw as a stop. When sliding the tube far in, the screw hits the speedring and prevents the tube from accidently sliding too far and falling through.

Speaking of sliding - let's look at:

How others slide the tube

First, I had a look at similar projects by others:

el_mambo has made a round disc out of teflon that (thanks to a few screws) fits into an Elinchrom bayonet. It has a round hole in the middle within which the tube is installed.

Oliver Krause disassembled a Bowens mount and attached a wooden disc to it, also with a hole.

Mikrosat have a commercial Bowens adaptor similar to Oliver's and Detlef's, but of solid metal. (I bought that one - it's very sturdy but ridiculously heavy. That was a no-go for use on location)

All of the above solutions have one thing in common: they mount into the existing speedring adapter, so there are four connected pieces: 1. the speedring, 2. the insert for the speedring (with a manufacturer specific bayonet), 3. the disc (with a bayonet mount to mount the insert), 4. the tube that goes inside the disc. Pretty complex! So let's make:

A simpler and lighter tube guide

There is no need for a bayonet mount in that speedring if you don't intend to mount a flash to it. Therefore I went for a simpler solution: instead of making a disc with a bayonet mount, I decided to make a bigger disc that replaces the insert altogether and mounts right into the speedring with the four screws.

Thus I CNC-milled a round disc out of aluminum with the outer dimensions of a typical speedring insert: 145mm diameter. (some manufacturers have smaller or bigger inserts, but this seems to be the most wide-spread size)

Next task: make a guide to fit the tube. Much to my delight, Stefan at FabLab Berlin gifted me a few left-over pieces of Polyoxymethylene (POM). POM is known for its low friction - which is just what I needed. I CNC-milled a rounded rectangular shape with a round hole in it (with the diameter of my tube), and I screwed two layers of that onto my aluminum disc.

In order to hold the tube in place when you don't want to slide it, I drilled a 2.5mm hole into the side of the POM part and cut an M3 thread into it. Now I can use a knurled head screw to lock the tube in place. (More about that screw see below)

Now the insert can be put into the speedring and held in place with the supplied four screws. And we can also insert the tube:

How to put it on a light stand

Sounds easy. But it actually is tricky, because the obvious solution is flawed. Since there is no spigot bolt or thread on the speedring, the first thought that naturally comes to mind is working with the tube that so nicely sticks out the back of the speedring. One could use a dual grip clamp (like you would for a boom):

The problem with this approach is that it makes focusing the reflector very cumbersome. After all, focusing is done by sliding the tube in and out of the speedring. But that would move the whole softbox, because the tube is fixed. So if you want to keep the softbox in the same place, you have to not only slide the tube in the speedring, but also re-adjust the grip clamp to a different position on the tube. That's a big hassle - therefore it was not an option for me.

Update: As Oliver just pointed out, I missed the fact that he is using a cut-off tripod in the clamp, so the boom arm itself is extensible (tube in tube) and does allow him to focus without changing the position. Very smart approach!

Another option I discarded is this one:

A speedring with a built-in tilting mechanism! (made by Aurora / Hensel). It's a great product as long as you only use it in the studio, or if your assistant carries it for you. For the rest of us, this piece of equipment is simply too heavy and too bulky. I ordered one, but I instantly returned it too the store, since it would have tripled the weight of my reflector and taken more space than two flash generators including batteries. Mind you, it's also quite deep (which the photo doesn't show).

As a solution, I disassembled one of those cheap swivel mounts with hotshoe that you can get from China for $10. There is a huge variety available, but note that some are more sturdy than others. After all, these swivels are designed to carry just a speedlite and a simple umbrella. If you want to put more weight on them, you first need to find a sturdy enough model. Those (see below) are fine:

It originally came with a hotshoe, which I removed. Instead I added the white plastic you can see on the picture (CNC milled from 12mm POM) as a spacer. That allows the swivel to tilt full way without prematurely hitting the speedring. I Attached it to my custom speedring insert with four M3 screws and voilà - the reflector can now be mounted on a light stand, tilted, and independently focused.

Alternative tube guide

I was worried that the screw which I use to hold the tube in place may damage the tube. If it makes a dent in the tube (so far my reasoning), maybe the tube will jam in its guide and not slide smoothly anymore. Therefore I decided to design a different tube guide where the screw locks the tube in place by pulling the plastic tight around it (and not by pressing directly against the tube). This is what my other design looks like:

It works. But it's not really better than the previous solution. As it turned out, with this design, the screw needs 3 full rotations to lock the tube. With the screw pressing against the tube, one single rotation does the job.

I also concluded that my worries had been baseless: the screw pressing against the tube does not harm the tube, at least not in a way that would affect its slidability. I attribute this to the guide being made of plastic. When the screw is fastened, the plastic bends very slightly outwards, which is perfect to lock the tube. In that respect, an elastic material like plastic is superior to a rigid metal, because it has a higher ability to clamp.

Moral of the story: I removed the diagonal screw, drilled another hole in the side of the plastic and put the screw through that one, like in my original design.

Dimensions and learnings

While making this device, I learnt a lot about proper dimensioning that I would also like to share with you:

Tube material and diameter

I made two different tubes (as you may have noticed, the alternative mount has a bigger diameter). Both tubes are aluminum tubes from my local hardware store.

The first tube has an outer diameter of 16mm (wall thickness 1mm). That's quite thin, but it's still thick enough to work fine. The more weight you put on the tube, the more it bends. And the more it bends, the more it gets jammed in the guide and the more the flash hangs down from the center. This was not an issue with the Elinchrom Quadra head, and a speedlight would also work well. But if you are going to mount anything heavier, or if you use a longer tube in a bigger softbox, you will need a thicker tube.

The other tube is 25mm in diameter (1.5mm wall thickness). It's pretty sturdy, but it's also heavier itself. This tube would be able to carry most flash heads in this reflector. If a bigger softbox is used and thus a longer tube is required, you should consider an even bigger diameter.

Thickness of speedring insert

The Aluminum I used for the speedring insert was 1mm thick (for the 16mm tube) and 1.5mm thick (for the 25mm tube). Since the swivel is attached to this disc, the disc carries the weight of the whole device and is prone to bend. While the force does not cause any visible bends, it's enough to slightly deform the tube mount which causes the tube to glide more sluggishly. For my project 1mm is still fine, 1.5mm can't be wrong to be safe. For bigger softboxes or heavier flashes, a stiffer (thicker) insert is required.

It's really light and small

I love shooting on location, and (as long as there is no wind) this is the perfect tool: the whole device weighs only 690 grams (1½ lbs). That includes everything but the flash head: the speedring, insert, swivel, tube, mount, softbox, rods and bag. Even if you add the Quadra head, the device is still below 1kg. And it all fits nicely into the bag that came with the softbox:

First results

I was only able to use it once so far. More photos will probably come later. For more from my model shootings visit Dennis Christian Fotografie!

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Commercial ringflash bracket all look alike. And they all suck. That's why I built my own.

Small, light, no frills, quick release.

The fundamental problem with most ringflash brackets is that they must fit a huge variety of cameras and lenses. All of which have different dimensions.

Commercial ringflash bracket all look alike. And they all suck. That's why I built my own.

Small, light, no frills, quick release.

The fundamental problem with most ringflash brackets is that they must fit a huge variety of cameras and lenses. All of which have different dimensions.

It must be possible to adjust the vertical position (depending on the distance from the camera base plate to the height of the optical axis). But it must also be possible to move the ring flash on the depth axis (i.e. closer to the camera or further away). Some people use short lenses, others use longer ones, many people need to reach a zoom ring on the lens, which is not possible when the ring flash sits just there. That's why these brackets are adjustable within a wide range. But this creates other problems: if the bracket is long enough to sit on the rim of a 70-200mm lens, then that means the bracket will stick in your face when you use a small 50mm lens. I find that extremely inconvenient.

Saving space and weight

I found that I don't need much adjustment on the depth axis, so I went for a design with a fixed depth position and only vertical adjustment. That makes the whole bracket must simpler. It's basically just a solid piece with no moving parts.

Another problem I found extremely annoying with conventional brackets is that they consist of two L-brackets connected through a bridge part under the camera. That bridge part takes a lot of space on either side, although it just serves the purpose to hold one screw in the middle. Why not go for a more space-saving design? (I'll tell you why: because even the distance between the L's is adjustable, to fit different ringflash models. That's why these brackets all look the same - it's a one-fits-all design. Good for the manufacturers, but meaningless for you if you just own one model. That would be like buying one-size-fits-all-clothes for the reason that anyone can wear them)

I shoot on location a lot, and I don't feel like disassembling and re-assembling half of my equipment all the time just because it takes a ridiculous amount of space in the bag if you leave it mounted. My own design does not overlap towards any side.

How to make one

First I measured all the relevant distances of my camera, my lenses and my ringflash. Then I drew the part in a CAD program and I CNC milled it out of 3mm Aluminum.

The slots allow for moderate vertical adjustment. On the bottom, the part has 5 holes for the center screw (just in case) but honestly I only ever used one.

Bending the part was tricky. I underestimated how much force is needed to bend 3mm thick Aluminum over a length of multiple centimeters. I thought that I could simply the part in a vise and bend it with large pliers and maybe a piece of wood along the edge. That turned out unfeasible, since I could hardly put enough pressure on it and the bend radius became much too big. Finally I did the trick by fixating the not-to-be-bent areas with thick steel profiles and using a 1 meter long piece of wood as a lever.

That first version was already usable, but it had somewhat sharp edges. I chose to paint it with black liquid rubber, for two reasons:

The rubber covers the sharp edges and prevents them from scratching or damaging stuff

The rubber makes the part very sticky, so it never slides away where other parts are attached to it.

Meet the Arca mount

Ringflash makers want you to screw the bracket to the bottom of your camera with a tripod screw. Is this how you mount your camera on a tripod? If not, why should you mount a ringflash this way? A quick release mount is much more convenient, and I have a quick release plate under my camera anyways, hence I bought an Arca-swiss compatible mount made by Sirui and screwed it to the bracket for good.

Conclusion

I am very content with this part. It can be adjusted in two dimensions. Very easily in one, and a (less conveniently) in the other. The adjustment ranges are within useful limits. Much less flexible than with the conventional mount, but hey: I adjusted it once and never ever needed to change it again.

The rubber coating is practical although not pretty. It doesn't look as nice as an industrially manufactured part, but who cares.

As you can see on two pictures below, I mounted it to the side of my camera. It can also be mounted to the bottom of the camera, but I always have an Arca L-bracket on my camera anyways, and mounted this way, the screws (of the ringflash) don't get in the way of my fingers when holding the camera. Furthermore, the camera rests better on a flat surface when it's mounted to the side.

In a potential version 2.0, I could even place the slots diagonally to get the screws in more convenient places.

Someone asked: How do you zoom your lenses when that thing is so close to the camera that you cannot reach the zoom ring? I don't. I only use my ringflash on my PhaseOne camera, and ALL my lenses for this camera are fixed focal length. There is no zoom.

See below for more pictures. By the way: I have one more bare aluminium part since I made two. It's slightly blemished but perfectly usable, and available for an affordable price to anyone interested. Or you can have the CAD file for free.

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I extensively compared 3 softboxes for the purpose of making a focusable deep parabolic reflector (with the light source attached to a focusable tube, not to the speedring as intended). This article sums up my results.

I extensively compared 3 softboxes for the purpose of making a focusable deep parabolic reflector (with the light source attached to a focusable tube, not to the speedring as intended). This article sums up my results.

A focusable parabolic reflector is…

…a light modifier with a parabolic shape that can be focused, i.e. the light source can be moved within the reflector. This allows very different light characteristics ranging from focused to wide-open. Besides this unique flexibility, other advantages of focusable parabolic reflectors are their high energy efficiency and the relative absence of hotspots.

Why make one out of a softbox?

Such reflectors are commercially available in uncompromised quality, however, their prices exceed the budgets even of many professionals. My goal was to make my own DIY focusable deep parabolic reflector based on a softbox (where the light source would not be attached to the speedring as intended, but to a focusable tube). I examined three softboxes regarding their fitness for this purpose. This article sums up my results.

The candidates

Aurora Tera-D 35
A deep, supposedly parabolic softbox with 16 rods.
Same diameter as the RimeLite (90cm) but even deeper

Elinchrom Rotalux Deep Octa 70cm
Elinchrom's popular softbox with folding speedring and 8 rods
Great for beauty lighting when used traditionally (as a softbox)

I considered taking parabolic umbrellas into this comparison as well, however I noticed that they are generally much more shallow than the softboxes, which means that the focal point is further away from the vertex (often far outside the umbrella). That's bad for spill and makes defocusing impractical. Furthermore, the mechanical parts of the umbrella are in the way which makes it hard to attach a focusing mechanism. That disqualifies these umbrellas for the purpose of my project. A fellow DIY maker, Detlef G. of Schwarzweissart has also reported stability issues with such umbrellas.

The method

The final goal of the project was of course a proper focusing mechanism, however that would depend on the choice of softbox, thus for this experiment I manually held the light source in place. The light source was an Elinchrom Quadra A Head, attached to a hand-held telescope rod (the „Long grip“ by Lastolite).

I tested four different positions per softbox:

The focused position (manually determined with the help of the modeling light as the point where the beam of light is most narrow)

The half-focused position (half-way between focused and de-focused)

The de-focused position (where the light furthest from the focus point while still on-axis and inside the reflector)

Direct light (light source inside the speedring, facing outside. The normal intended use case of the softbox, but without any diffusors)

Test case 4 is very different from a focusable parabolic reflector since the light is facing the other direction. It is the normal use case of a softbox but without the softening diffusors. I just tested this as well to determine how the focusable reflector compares to a normal softbox without diffusors, and whether making such an extravagant light modifier is even worth the hassle.

For test cases 1 through 3 I closed the hole in the speedring with aluminum foil so that light would reflect back also from the center (where most of it hits when focused).

A focusable parabolic reflector is obviously an indirect light source, so direct light from the flash was not desired in positions 1-3. I tested two configurations per position and per softbox: one of a bare flash head flashing into the softbox, and one of the flash head equipped with a small metal disc shielding direct light (I used the Lastolite Quadra adaptor for Ezybox, which is basically just an aluminum disc with a bayonet):

The biggest white surface I had available to be lit was a ceiling in a high room, so I put the softbox between two chairs, facing upwards towards that ceiling. The softbox was about 50cm from the floor and the room height is 420cm, thus the distance of the ceiling was 370cm from the innermost point of the softbox.

There are two minor shortcomings of this approach:

The ceiling is not completely flat, but slightly diagonal and rounded on one side (the left side). This leads to a little distortion of the light spot and slightly brighter light on the left side due to the rounded part being a bit closer than a flat ceiling would have been. Having that in mind, it’s not a big deal, especially since the softboxes are symmetrical and the other side of the pictures is unaffected

There is a window front on the back wall (bottom of the frame) which reflects some of the light back onto the ceiling. The reflectiveness of window glass is supposedly 3%, thus the effect is not strong, but nevertheless it is visible on some of the test shots. Fortunately the windows have window frames that do not reflect and the reflection of the glass is hard (undiffused) so it can clearly be seen on the photos how bright the ceiling would be without the reflection from the glass, by simply looking at the parts where reflection is absent due to the window frames.

The camera was an Olympus E-M1 with a 14mm lens (corresponding to 28mm on a full-frame DSLR), f/8, 1/100s. The camera was placed on a small tripod on the floor, about 150cm distant from the softbox, facing the point on the ceiling right over the softbox. A test shot was made without flash to ensure that the frame at these settings is completely black and all the light on the test shots indeed results from the flash and not from ambient light.

The results

Let's see pictures. By the way, the round thing in the top right corner is a stair-case from below and the funny guy in the bottom left corner is me holding the flash rod into the softboxes. Just the perspective is somewhat unusual.

Rime

Aurora

Elinchrom

Focused Disc

Focused Bare

Half-Focused Disc

Half-Focused Bare

De-Focused Disc

De-Focused Bare

Direct

Interpretation

General conclusions:

All of the tested softboxes can be used with different positions of indirect light to somewhat achieve the desired result, however the quality of the results varies a lot.

It hardly makes a difference whether a disc is attached to the flash or not. Well, we see only brightness on plain surface here. I can imagine that it does make a difference in shadows. In any case it cannot be wrong to avoid direct light on the subject, so a little screen is probably a good idea but it need not be big.

Direct light through the speedring of any softbox without a diffuser is just plain ugly. It's simply not a good idea to do that, especially because of the hard falloff edges. The learning here: test case 4 was pointless. If at all, the indirect parabolic lighting should have been compared to a regular softbox with at least one diffusor.

The Elinchrom Deep Octa suffers from two conceptual weaknesses: first, it has only 8 rods while the other two candidates have twice at much and are thus much rounder. Second, it's not even a parabolic softbox by design. That makes it difficult to focus the light since the softbox simply has no single focal point. In the de-focused setting, the result is quite pleasing (although it has a hotspot). But while manually trying to find the point where the light is most focused, I noticed that the further I moved the light into the softbox, the more focused it looked but also the harder the edge of the spot became. The visible edge in the spot of light is a shadow thrown by the rim of the softbox which is blocking light from the opposite side. I also attribute that to the non-parabolic design. And as a side effect, the would-be focused light is considerably darker than with the other softboxes, because some of it gets reflected across the whole room. Just to get one thing clear: this is not a bad softbox. In fact, it's my favorite softbox and performs wonderfully when used as intended. But as this test shows, the Deep Octa 70 is not fit for the purpose of a focusable parabolic reflector, because it is not focusable.

While the Aurora performs better focused, it disappoints in the half-focused setting. I was quite surprised to see a dark halo. It's even visible in the focused setting, but strongest in the half-focused one. Obviously this softbox focuses some of the light in a middle hotspot and throws more light towards the sides, but the falloff is nothing like a nice poisson curve; it is not even continuous. From the middle towards the sides, the light gets darker, then brighter again and then again darker. And not just by a bit - the deviation from the expected steady decline is a whole stop of exposure and can hardly be ignored. That makes this softbox unfit for practically all applications where a half-focused setting is desired. Why does this happen? I would guess that its shape is a little too round, but honestly, I don't know. One would have to calculate the reflections. But the images speak for themselves. Quite a pity, since this softbox has the highest build quality of all three and is also the sturdiest. A bit heavy maybe, and hard to (dis)assemble, but still quite convincing as far as handling is concerned. Nevertheless my conclusion: not first choice for a DIY parabolic reflector.

That leaves us with the RimeLite Grandbox, which delivered the most convincing results. In the focused setting, the light comes closest to a hotspot with a nice steady falloff. This softbox also produced the brightest spot (hence its ability to focus is the highest). In the half- and de-focused positions, the brightness is subject to subtle local variation, probably resulting from the hexadecagonal shape of the softbox and wrinkles in the material. A little bit of a dark halo can also be seen in the half-focused setting, but much less so than with the Aurora. That makes the RimeLite the clear winner of this test. In terms of handling, the softbox is very light and quickly assembled, however it's also the most fragile of the three. Fine for outdoor applications, but just as long as there is not much wind. It doesn't take much to deform this softbox, especially since we're not using any diffusors that would add extra stability. Somewhat stronger rods would have been a good idea. And the reflective material is also the one throwing most wrinkles - considerably more than the Aurora or the Elinchrom. It's light though. For a DIY focusable parabolic reflector, the RimeLite is my clear favorite out of these three softboxes.

Further reading

While this has been a comparative analysis of three softboxes and we have merely looked at visual results, Detlef G. has chosen just one softbox (duh... the same one :), conducted extensive measurements with a light meter and graphed his results, outlining the different lighting characteristics of the three positions. I highly recommend his article on the subject.

Why are parabolas so hard to achieve?

After I attributed most of the above mentioned problems to the shape of the softboxes, I started wondering why the heck they're not simply made to be accurately parabolic. It's apparently harder than it sounds to build a true parabolic softbox. Think about bending a metal rod: the naturally resulting shape will be an arc, not a parabola. If you want to bend it parabolically, you need considerably more force near the vortex. Basically that could be achieved by the surrounding tissue, but that again would put a lot of pressure onto small parts of the tissue and especially the seams.

If you think about how to avoid these problems, a promising approach would be to separate the rods from the reflective material by adding a T-shaped section to each rod. The rods could then run outside the actual reflector in a more rounded arc shape while the reflector inside could be accurately parabolic. It seems that I'm not the first person to have this idea: some of the unaffordable high end parabolic reflectors look quite similar to this.

In any case, we can learn a few things from this thought experiment:

Accurate parabolic shape is an important quality criteria for a parabolic reflector as it directly affects the ability to focus and thus the quality of the light

Building accurate parabolic reflectors is a challenge. While it's straight-forward to construct a roughly (approximately) parabolic softbox, constructing a perfectly accurate parabolic softbox calls for a considerably more complex and thus more expensive design due to mechanical reasons.

Therefore we should not assume that anything labeled "parabolic" is actually parabolic of even comparable. First of all, it's marketing. That's why tests like this one really make sense.

A custom Sev5n filter box for 75x90mm filters.

I made my own because nobody makes those commercially. It's compact, light and sturdy. Here's how to do it.

What makes a good filter case?

Slide-in filters are probably the most useful accessory for landscape photography (besides a good tripod). With those fragile rectangular pieces of resin or glass comes the need to store them. A good filter storage system should

prevent filters from collecting dust and dirt

protect filters from scratches (especially resin filters)

protect filters from breaking (especially glass filters)

allow you to quickly and easily access a particular filter and to store it again after use, preferably with one hand, so you can concentrate on taking photos

be light-weight and small in your camera bag

Some people use those CD-wallet-like pouches that open like books and are intended for round screw-in filters. I'm not a fan of those, since it's too cumbersome to find the filter you need. Other pouches unfold like a long scroll. That's not feasible in windy conditions or when you have no place to put it on wet or dirty ground. The best case I found for my large (6x4" / 100mm / "Z-Pro") filters that I use with my Canon 5Dii is the Kinesis F169 Filter pouch... but that's one-size-fits-all and much too big for Seven5.

What about Seven5?

When I got my mirrorless camera (the Olympus OM-D E-M1), I noticed that my existing filters are less than ideal for the small MicroFourThirds lenses. Sure they're usable, but the gradients are too soft and the filters take too much space in a stream-lined small bag. What I needed are the smaller 75x90mm (3x3.5") filters. Lee calls them Sev5n but Singh-Ray and some other manufacturers make them too.

I found that there is not a single filter pouch or box available on the market for filters of this size. Really, none! So I made one. Here's how.

Soft pouch or hard case?

First I had to decide whether I wanted a soft bag or a hard case. I thought about sewing a soft pouch (like the Kinesis) from micro-fiber lens-cleaning cloth with thin layers of PVC between it (simply cut PVC folders to the desired size) to keep the shape. Then however I decided to go for a hard case. My reasoning was that when nothing touches the filters' surface, they run the lowest risk of being damaged.

3D printing was not accurate enough

My first attempt was 3D printing. Using a 3D CAD program, I designed the parts for the sides which have a little grid of spacers that hold the filters apart. I could have printed the whole case as one single part, however that would have taken forever and used up too much filament, so I decided to only print the complicated side parts and add simple rectangular acrylic parts as covers from three sides.

I decided to print the parts standing (as opposed to lying) because I wanted the guides to consist of many layers and not just one layer of filament that can easily break off. When starting to print, I was concerned about two things:

The overlapping bit that later holds the ground cover needs to be printed "in the air" - is that feasible?

If I print the part standing, is it at risk of falling over?

It turned out that both were not a problem. The slicer I used (MakerBot MakerWare) did a good job of generating easily removable support material for the overlapping part, and thanks to a raft on the build plate, the part stood very stable.

The problem however turned out to be a different one: the printer's accuracy. I had designed the guides between the filters to be 0.4mm thick (which is one layer of filament on the MakerBot Replicator 2. The printer however oozed extruded filament all over the place, causing some filter slots to be almost half a millimeter thinner than designed. I cleaned it up a bit, but it's still visible on the photo. That was not accurate enough. After some thinking I came to the conclusion that 3D printing is not the prefered technology for this project and I moved on to attempt #2:

CNC milling the guides

Designing side parts with guides for CNC milling is not a terribly complicated task. But since the CNC router I have access to is just a 2.5 axis machine, I would have to do without the fancy rounded corners (unless I wanted to spend a lot of extra time on turning the part around, re-aligning and fixing it again). So here's version 2 (I didn't even draw it in 3D, I went straight from the 2D drawing to the CAM tool, Cut2D):

As a material for this part I chose 12mm Polyoxymethylene (a.k.a. Polyacetal or POM). I'm usually a fan of aluminum, but in terms of scratching the resin filters, metal would probably not be a good idea. POM is my prefered plastic (I'll soon write an arcticle about it) and turned out to be a good choice for this project as well. Here's a fancy video of the parts being milled by the BZT PFE 1000 PX at FabLab Berlin:

And the milled parts before being removed from the surrounding material (they're only dirty but very accurate):

And I made an old mistake again: I didn't cut all the way through. That's because plastics have a huge positive tolerance and my 12mm POM plate was actually 12.7mm thick. A utility knife did a good job in cleaning up the edges.

Laser-cutting the covers

I could have milled the covers as well, but since I had always wanted to use a laser cutter, I gave that a try. Ridiculously easy, it turned out, and the cuts were very clean and shiny. Material is 3mm acrylic. The cutter is a Epilog Zing 6030 set at 80% power, 40% speed in VisiCut:

Assembling the case

All parts done, let's put them together.

I hadn't worried about how to put the parts together, but the first intuitive approach was glueing. Now POM is known to be hard to glue since most adhesives don't stick to it. There are special purpose glues which can glue POM, but I didn't have any - I was glueless, so to speak. I decided to just try my trusted Cyanoacrylate and, in case it wouldn't stick, drill some holes and screw the parts together. Cyanoacrylate sticked well though.

As a means of accessing the filters for removal, I had planned to put a little strip into the box under the filters, like a bookmark, that, when pulled, would lift the filters. But I found that simply leaving the bottom side open does just as well, as long as the bottom is somehow protected against dirt.

(No, it's not a toaster!)

What's inside

I could glue an index paper to the top of the case, revealing which filter is in each slot. But I don't really need it, since unlike the big Kinesis pouch, this case with its contents looks very characteristic and I can easily remember what these are (bottom to top):

2-stop soft grad ND

3-stop soft grad ND

4-stop soft grad ND

empty

1-stop hard grad ND

2-stop hard grad ND

3-stop hard grad ND

2-stop reverse grad ND

3-stop reverse grad ND

10-stop solid ND

As it turns out, Manfrotto makes a little pouch intended for point and shoot cameras that's perfect for my new filter case, the Seven5 filter holder and the clip-on polarizer: